BlenderKit Asset Bar turns black
Answering my own question after the issue went away without any intended action.
The bug tracking tool at https://developer.blender.org/ is a better source of information for such issues: a search for &quot;blenderkit&quot; reveals that other users had similar issues (not working, not displayed, even crashed), but many of these trouble tickets were then abandoned by the reporter.
https://wiki.blender.org/wiki/Process/Bug_Reports and https://youtu.be/JTD0OJq_rF4 are great sources on what to consider while debugging/reporting.